She believes government plans to teach children to read even earlier, at pre-school, are a mistake.

The government insists children are starting school at the best time, and says early years learning involves play-based as well as formal learning.

Ministers are striving to improve reading standards across all age groups.

Dr Katz, a professor of education at the University of Illinois in the USA, thinks policy makers are pushing children too hard too early.

Most youngsters in the UK start learning to read and write in reception when they start primary school - often before their fifth birthday.

In Scandinavian countries formal teaching begins much later, usually when children are six or seven.

The evidence... suggests starting formal instruction early is more damaging for boys than girls

Professor Lilian Katz, professor of education, University of Illinois

Dr Katz, who was addressing an international conference on foundation-stage learning at the University of Oxford, said there was a danger that the British model could put children off reading for life if pupils were forced to learn before they were ready.

She said: "The evidence we have so far is that if you start formal teaching of reading very early the children do well in tests but when you follow them up to the age of 11 or 12 they don't do better than those who have had a more informal approach.

"The evidence also suggests starting formal instruction early is more damaging for boys than girls.

"Boys are expected to be active and assertive but during formal instruction they are being passive not active.

"In most cultures, girls learn to put up with passivity earlier and better than boys."

Pre-school demands

She suggests a more informal approach tuned in to children's "natural nosiness" is much better and cites the example of children going to visit a local bakery and then writing down what they have seen and experienced.

"Vocabulary must be learnt in context," she asserted.

Dr Katz - who lectures around the world on early years education - also emphasises that English is a very difficult language to learn.

"What's the hurry?" she said.

"Some people think that because English is so difficult you should start early but that's wrong. If it is so difficult wait until they're older and do it in a natural context - where they see things and write them down."

Children should be introduced to the alphabet at the age of about five-and-a-half, in an ideal world, said Dr Katz.

But the government is planning to introduce more structured learning for three and four year-olds in pre-school which will set new learning goals, including one which specifies that by the time children start school they should be able to at least "use their phonic knowledge to write simple regular words".

Dr Katz does not support this approach.

She said: "Academic instruction isn't necessary in pre-school."

Her comments come as concerns grow over young people's reading skills.

In England, a quarter of all 14-year-olds fail to reach national standards and boys are falling even further behind.

Responding to Dr Katz's comments, a Department for Children, Schools and Families spokesman said: "We want all children to make progress in literacy and numeracy at an early age, as these skills are critical to their ability to get the most out of learning later on.

"The formal school starting age of five has served children well for decades and standards in our primary schools have never been higher. Key stage results and Ofsted reports make this clear.

"The first years of schooling focus on play-based activities in addition to formal learning. The curriculum is age-appropriate and we actively support teachers to adapt their teaching to the needs of children."